1. Field of the Invention.
This invention relates generally to fill valves and containers for containing fluids and, more particularly but without limitation, to fill valves and containers for containing fluids such as propane, butane, and the like.
2. Description of the Related Art.
A common occurrence is the filling of containers with fuel or other fluids, such as portable propane tanks for barbecue equipment for example. A common procedure for filling such a tank, wherein the weight of the tank is generally visibly stamped on its outer surface, is to place the tank on scales set at a particular weight, such as twenty pounds plus the empty or tare weight of the tank. As the tank is being filled, someone watches the scales; when the balance indicates that the weight of the tank and its contents is equal to the setting on the scales, filling of the tank is terminated.
Presumably, the tank then holds the desired twenty pounds of fluid. Unfortunately, that may not be the case. For instance, the weight stamped on the tank may not be equal to the weight that would be observed if the tank were totally empty. If the tank has mud or other debris adhering thereto such that the stamped weight is less than the empty weight of the tank at the time of filling, the patron will get less than his money's worth because he will be paying for propane that he is not receiving, namely the weight of propane equal to the weight of the debris. Further, the scales may not be properly calibrated or balanced, or the scales may be set at a reading of less than tare weight plus twenty pounds, particularly if the patron is not positioned whereby the filling attendant's activities can be closely observed. As a result, the patron may again be getting less than his money's worth.
Conversely, a careless or over-busy attendant may permit a patron to fill his own tank. In that situation, the patron may be tempted to get more than his money's worth and introduce more than twenty pounds of propane into the tank, which may present a serious safety problem. The volumes of many fluids, such as butane, propane, etc., are temperature dependent. For example, the volume of a given weight of propane increases approximately one percent for each temperature increase of approximately 5-6.degree. F. Thus, as the temperature of propane increases, the weight or mass of propane that can be placed in a given volume at a given pressure decreases. By the same token, the pressure of a given weight of a temperature-dependent fluid placed in a closed container at a given temperature may substantially increase as the temperature of the fluid increases.
As a more specific example, the pressure of liquid/vapor phase propane at -44.degree. F. is approximately zero psig and at 100.degree. F. is approximately 172 psig, or a pressure change of 172 psig for a temperature change of 144.degree. F. However, a temperature increase of 1.degree. F. in liquid-phase only propane may cause a pressure increase in excess of 500 psig.
Therefore, what is needed is a device, and a container having such a device, that determines a certain "filled" condition of the container as fluid is being introduced thereinto by detecting the containment of a predetermined weight of fluid in the container; that automatically prevents further filling of the container beyond such a "filled" condition; that prevents further filling of the container beyond such a "filled" condition even though conduct to thwart such a device is attempted by inducing inertial effects therein; that is substantially independent of the composition, pressure, and/or temperature of the fluid being introduced into and/or contained by the container; that is immune to errors in scales or tare weight of the container; that prevents introduction of fluid into the container unless the container has a essentially upright orientation; and that controls flow into the container with a pressure that has a substantially smaller magnitude than the pressure at which fluid is being introduced into the container.